As it is known in the optical communications art, light signals can be modulated in accordance with associated data signals such that the information is optically conveyed between a transmitter and a receiver. In order for that optical data to be accurately and efficiently transmitted, the undesirable reflected light, or optical noise, generated within optical components that make up the transmission, amplification, and receiving systems should be minimized. Without minimizing optical background noise levels, difficulties are encountered when trying to maximize the quality of the optical signals and the quantity of information carried by those optical signals. Undesirable reflections cause degradation in optical performance in many ways. Three of these degradation mechanisms (noise, interference, and feedback) are particularly worrisome for sealed opto-electronics modules or packages. More precisely, xe2x80x98noisexe2x80x99 from undesirable reflected light can be characterized as stray or scattered light impacting optical detectors and monitors inside opto-electronic packages. xe2x80x98Interferencexe2x80x99 from undesirable reflected light involves light unintentionally entering passive optical components such as waveguides. xe2x80x98Feedbackxe2x80x99 from undesirable reflected light is unwanted but relatively highly concentrated reflected light reentering the optical path.
Many modem optical components are extremely sensitive to stray or scattered reflected light generated by active components located inside the same opto-electronics module. As the performance of opto-electronics components improves, means to improve the accuracy of these sensitive components becomes desirable and one manner to do so is to reduce the amount of undesirable reflected light in the package.
Two common prior art approaches, referred to as component angling and component shielding, have been used in the past to limit the effect of undesirable light in opto-electronics packages. Angling components takes advantage of the law of regular reflection that dictates that a shiny object reflects most light coming in at a particular angle of incidence away at a specific angle of reflectance (for example, reflections from a mirror). Angling components allows some degree of control over concentrated beams of light, enabling a design to be configured to reflect undesirable light away from sensitive components.
Shielding involves placing physical barriers between undesirable reflected light and sensitive optical components. The classic example of shielding in telecommunications applications is the use of multiple, discrete opto-electronic modules connected by fiber to separate light sensitive components from light generating components.
In accordance with an aspect of the present invention, a method and apparatus are provided for eliminating or reducing undesirable reflected light in opto-electronic packages. Such an effect is achieved through disposing a light absorbing material on selected inner surfaces of the opto-electronic package such that light incident on the material is not further reflected within the package to any significant degree. With another aspect of the present invention, the light absorbing material should be selected such that it does not give off significant particulate matter in quantities significant to interfere with the operation of the opto-electronic package, should not outgas moisture or hydrocarbons in quantities significant to interfere with the operation of the opto-electronic package. One example of such a material can be pieces of Germanium.